There have been attempts to use movement of the human eye to monitor involuntary conditions, specifically a person's wakefulness or drowsiness. For example, U.S. Pat. No. 3,863,243 discloses a device that sounds an alarm to warn a person using the device that they are beginning to fall asleep. The device includes a frame similar to a set of eyeglasses onto which is mounted a fiber optic bundle and a photocell that are directed towards the user's eye when the frame is worn. The fiber optic bundle is coupled to a source of light and a pulse generator to emit light towards the user's eye.
The photocell detects the intensity of light reflected off of the user's eye, i.e., either by the eyelid when the eye is closed or the eye surface when the eye is open. Circuitry receives a signal from the photocell, and uses a timer to distinguish between regular blinks, and an extended time period during which the eye is closed, i.e., a time period that may indicate that the person is falling asleep. When a threshold time elapses, an alarm is sounded to notify and/or wake the user. This device, however, requires running wires and fiber optic bundles from the frame to external components, e.g., the pulse generator and the required circuitry, and for this reason, the device may be awkward or inconvenient to use.
Other devices, such as those disclosed in U.S. Pat. Nos. 5,469,143 and 4,359,724, directly engage the eyelid or eyebrow of a user to detect movement of the eye and activate an alarm when a drowsiness condition is detected. These mechanical devices may be mounted directly onto the skin to detect muscle movement or may involve placing a mechanical arm against the eyelid, and consequently may be uncomfortable to wear and use.
In addition, some devices may detect eye movement, but may not be able to distinguish when the eye is opened or closed. For example, it may be desirable to measure the percentage of total time that the eyelids are closed as a function of time or the area of the palpebral fissure that is covered by the eyelid as the eye is opened or closed, commonly known as “PERCLOS,” for example during medical research or when monitoring driver alertness. Devices that merely detect eye muscle movement or eyelash movement may not be able to distinguish when the eye is open or closed, and consequently may not be able to measure PERCLOS. Similarly, such devices may not measure other parameters, such as velocity of eyelid closing or opening, acceleration or deceleration characteristics, duration of open or closed eye states, intervals between eye blinks and/or partial versus full eye blinks or eye closures.
Further, infrared cameras or other devices may be used to monitor a driver's awareness, which are typically mounted on the dashboard, roof or other fixed mounting within the user's vehicle. Such devices, however, require that the user maintain constant eye contact with the camera. In addition, they do not monitor eyelid movement if the user looks sideways or downwards, turns around, exits the vehicle or compartment in which he or she is being monitored, or if the camera moves relative to the individual. Further, such cameras may have problems seeing through eyeglasses, sunglasses, or even contact lenses, and may not operate effectively in sunlight.
Accordingly, it is believed that a more effective system and method for monitoring eye and/or eyelid movement would be considered useful.